Liquid developer for latent electrostatic images

ABSTRACT

The storage stability of a metal drier-containing liquid developer for latent electrostatic images is improved by the addition of an aryl-alkyl phosphite.

United States Patent [191 Westdale Oct. 14, 1975 LIQUID DEVELOPER FOR LATENT ELECTROSTATIC IMAGES [21] Appl. No.: 441,635

[52] US. Cl. 252/62.l [51] Int. Cl. G03G 9/00 [58] Field of Search 96/1 SD, 66.4; 252/621;

[56] References Cited UNITED STATES PATENTS 3,057,721 10/1962 Cowden et a1 96/664 3,681,243 8/1972 Okuno et a1. 252/621 L 3,839,045 10/1974 Brown 96/664 Primary Examiner-Norman G. Torchin Assistant Examiner.lohn L. Goodrow [57] ABSTRACT The storage stability of a metal drier-containing liquid developer for latent electrostatic images is improved by the addition of an aryl-alkyl phosphite.

4 Claims, N0 Drawings LIQUID DEVELOPER FOR LATENT ELECTROSTATIC IMAGES BACKGROUND OF THE INVENTION This invention relates to the art of electrophotography and more particularly, to a liquid developer for latent electrostatic images.

Liquid developer compositions, as used by the prior art, generally contain a colorant, comprising toner particles, and optionally, a dye; a resin which acts to bond the colorant to the electrostatic image-bearing substrate; and a vehicle which is composed predominantly of an insulating carrier liquid for the colorant, but which may also comprise wetting agents and an orientation aid.

According to a more recent prior art development, it has been found that the incorporation of metal driers, particularly metallic soaps, improve the images produced from liquid developers by either reinforcing the charge on the toner particles or by reversing the charge on the toner particles. This results in sharper, denser image areas and background areas relatively free of randomly deposited toner particles.

Metal driers which may be useful in the practice of the present invention include the resinates, naphthenates, oleates, octoates and neodecanoates of lead, calcium, manganese, cobalt, tin, copper, zinc, indium and zirconium.

Off-setting the advantages, obtained by the incorporation of metallic driers in liquid developer compositions, is the fact that these very additives tend to reduce the shelf-life of the liquid developer compositions by a substantial factor.

After storage for a period of as little as four months, metal drier-containing liquid developers produce images which are comparable to those produced with similar compositions from which a metal drier has been omitted. This is to say that the images are low in contrast, fuzzy, and with significant deposit of colorant in background areas.

The incorporation of conventional antioxidants, such as 2,6 ditertiary butyl p-cresol and butylhydroxy toluene are not effective stabilizers.

SUMMARY OF THE INVENTION It has been found, however, in accordance with the present invention, that metal drier-containing liquid developers can be satisfactorily stabilized by the addition of an aryl-alkyl phosphite ester of the formula:

where R, is an aryl, R is an alkyl and R is selected from the group consisting of R, and R It is therefore an object of the present invention to provide an improved liquid developer for latent electrostatic images.

A further object ofthe invention is to provide a metal drier-containing liquid developer with increased storage stability.

A further object of the invention is to provide a metal drier-containing liquid developer with a stabilizing quality of an aryl-alkyl phosphite ester of formula:

where R is an aryl, R is an alkyl and R is selected from the group consisting of R and R These and other objects and advantages of the present invention will become apparent from the following detailed description which includes a disclosure of the best mode contemplated for practicing the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS In accordance with one. aspect of the invention, there is provided, as a liquid developer for latent electrostatic images having improved storage stability, a composition comprising a resin, a colorant, a vehicle, a metal drier, and antioxidant, and an aryl-alkyl phosphite ester of the formula:

where R is an aryl, R is an alkyl and R is selected from the group consisting of R and R In accordance with a more specific aspect of the present invention, there is provided, as a liquid developer for latent electrostatic images having improved storage stability, a composition comprising from about .05 to about 0.20 wt. resin, from about 0.03 to about O.l 1 wt. colorant, from about 99.40 to about 99.85 wt. vehicle, from about 0.03 to about 0.I0 wt. metal drier, from about 0.04 to about 1.0 wt. antioxidant, and from about 0.01 to about 0.50 wt. arylalkyl phosphite ester of the formula:

O-Ri

where R; is an aryl, R is an alkyl and R is selected from the group consisting of R and R In a preferred form of the invention, R is selected from the group consisting of phenyl and alkyl phenyl wherein the alkyl contains up to ten carbon atoms, and R is selected from the group of alkyl containing up to 10 carbon atoms.

Suitable resins which may be used in the liquid developer compositions of the present invention include polyurethanes, alkyds, styrenes, natural resins, rosins and waxes.

The principal colorant ingredient as noted above is a particulate toner, for example carbon black, iron oxide or the like. The colorant ingredient may also comprise a dye which functions to change the color of the toner particles from a brownish-black to a bluish-black, to provide an image of higher contrast against a white background.

The vehicle comprises predominantly an insulating liquid carrier, preferably of the mineral spirit type, but may additionally include wetting agents, dispersants for the toner particles, and a particle orientation aid.

The metal drier is preferably a metal soap such as manganese naphthenate, manganese octoate and manganese neodecanoate, as well as the corresponding tin and cobalt soaps. Other metal driers which may be used include the resinates and oleates of the foregoing metals as well as corresponding compounds of lead, calcium, copper, zinc and indium.

Specific examples of antioxidants which may be used include 2,6 ditertiary butyl p-cresol, and butylhydroxy toluene.

Useful aryl-alkyl phosphite esters falling within the formula described hereinabove include diphenyl isooctyl phosphite, nonylphenyl di-n-propyl phosphite, phenol bis(2-ethyl butyl) phosphite, diphenyl Z-ethylbutyl phosphite, diphenyl n-butyl phosphite, diphenyl secbutyl phosphite, diphenyl n-hexyl phosphite, diphenyl 2-ethylbutyl phosphite, diphenyl n-octyl phosphite, diphenyl iso-decyl phosphite, di-p-cresyl 2-ethylbutyl phosphite, bis (p-tert-amyl phenol) 2-ethylbutyl phosphite, bis (p-tert-octyl phenol) 2-ethylbutyl phosphite.

A suitable commercially available material is Thermolite 187 sold by M & T Chemicals Inc.

EXAMPLE I A liquid developer concentrate was prepared from the following ingredients:

P-cresol (Shell Chemical Company) *oricntalion aid. "45% carbon black. 13% wetting agent. 42 7: solvent.

The polyurethane resin and alkyl blue were mixed on a high speed dispersator at 3,500 rpm for 15 minutes. One-half of the quantity of Magee oil was added very slowly with mixing for fifteen minutes at 1,000 rpm. The remainder of the oil was then added with mixing for 15 minutes at 1,000 rpm. The mixture was then set aside.

The lsopar H and lonol were admixed for five minutes to dissolve the antioxidant. This mixture was then added to the mixture of resin, alkyl blue and oil.

A half gallon of this last mentioned mixture was then added to the co-dispersion of carbon black very slowly with mixing for minutes at 1,750 rpm. This material was then added to the remaining portion of the mixture of resin, alkyl blue, oil, lsopar H and lonol, with mixing for 30 minutes at 3,500 rpm.

EXAMPLE [I 2200 ml. lsopar G 70 ml. toner concentrate of Example I 1.70 gms. manganese neodecanoate .82 gms. lonol 3.0 gms. Thermolite 187 EXAMPLE III A composition similar to that of Example II was prepared except that the Thermolite was omitted.

EXAMPLE IV The compositions set forth in Examples II and Ill were bottled and left in storage for 4 months, following which each was used as a developer composition in an electrostatic duplicating machine. Copies produced from the developer composition of Example I] showed the printed areas to be dark and crisp, and the background area to be relatively free of colorant. Copies produced from the developer composition of Example III were grayish, fuzzy, and the background area had a decidedly gray cast indicating substantial background deposition of colorant. The poor quality of the prints resulting from the developer of Example "I is believed to have resulted from a loss of effectiveness of the metal drier due to its decomposition or decay during 4 months storage.

The quantity of aryl-alkyl phosphite required to effect stabilization will vary in accordance with the type and concentration of metal drier. In general, however, it has been found that phosphite concentrations within the range of about 0.01 to about 0.5 wt. of liquid developer composition is satisfactory for the purposes of the invention.

Having thus described our invention, we claim:

1. As a liquid developer for latent electrostatic images having improved storage stability, a composition comprising a resin, a colorant, a vehicle, a metal drier, an antioxidant and an aryl-alkyl phosphite ester of the formula:

where R, is an aryl, R is an alkyl and R is selected from the group consisting of R, and R 2. The liquid developer defined in claim 1 wherein R, is selected from the group consisting of phenyl and alkylphenyl wherein the alkyl contains up to 10 carbon atoms, and R is selected from the group of alkyl containing up to 10 carbon atoms.

3. As a liquid developer for latent electrostatic images having improved storage stability, a composition comprising from about 0.05 to about 0.20 wt. resin, from about 0.03 to about 0.11 wt. colorant, from about 99.40 to about 99.85 wt. vehicle, from about 0.03 to about 0.10 wt. metal drier, from about 0.04 to about 1.0 wt. antioxidant, and from about 0.01 to about 0.50 wt. aryl-alkyl phosphite ester of the formula:

where R, is an aryl, R is an alkyl and R is selected from the group consisting of R, and R 4. The liquid developer defined in claim 3 wherein R, is selected from the group consisting of phenyl and alkylphenyl wherein the alkyl contains up to 10 carbon atoms, and R is selected from the group of alkyl containing up to 10 carbon atoms. 

1. AS A LIQUID DEVELOPER FOR LATENT ELECTROSTATIC IMAGES HAVING IMPROVED STORAGE STABILITY, A COMPOSITION COMPRISING A RESIN, A COLORANT, A VEHICLE, A MTAL DRIER, AN ANTIOXIDANT AND AN ARYL-ALKYL PHOSPHITE ESTER OF THE FORMULA
 2. The liquid developer defined in claim 1 wherein R1 is selected from the group consisting of phenyl and alkylphenyl wherein the alkyl contains up to 10 carbon atoms, and R2 is selected from the group of alkyl containing up to 10 carbon atoms.
 3. As a liquid developer for latent electrostatic images having improved storage stability, a composition comprising from about 0.05 to about 0.20 wt. % resin, from about 0.03 to about 0.11 wt. % colorant, from about 99.40 to about 99.85 wt. % vehicle, from about 0.03 to about 0.10 wt. % metal drier, from about 0.04 to about 1.0 wt. % antioxidant, and from about 0.01 to about 0.50 wt. % aryl-alkyl phosphite ester of the formula:
 4. The liquid developer defined in claim 3 wherein R1 is selected from the group consisting of phenyl and alkylphenyl wherein the alkyl contains up to 10 carbon atoms, and R2 is selected from the group of alkyl containing up to 10 carbon atoms. 